Aluminum photolithographic plate and method of imaging same



Oct. 18, 1966 F. A. REGAN, J-R., ETAL 3,279,366

ALUMINUM PHOTOLITHOGRAPHIC PLATE AND METHOD OF IMAGING SAME OriginalFiled March 31, 1955 Fire. 1

LITH06RAPHIC PzArE GELAT/N COA TING WITH SILVER HAL/DE gas-5511557 0FflCETATE l0 ALUMINUM 5HEET H EXPOSED GEMT/N W LAYER CON THIN/N6LEADACETATE LATENT IMAGE 0F SOD/UMSULF/DE SILVER HAL/DE ALUM- SHEETDEVELOPING AND FIXING BATH LATENT/MAGf 0F S/L v52 HAL/DE GELAT/AICOATING w/m EXPOSED SILVER HAl/DE 11v VEA/TORS BASES/1E Francis APgganynSeaman A. Lmcoln EXPOSED PHOTO. NEG.

51 Donald E, ansorz %Q7z// M YM Clifys' United States Patent 8 Claims.c1. 101-149.2

This is a division of our copending application Ser. No. 498,192, filedMarch 31, 1955, and entitled Method of Imaging a Photolithographic Plateand Elements for use in the Preparation of Same.

This invention relates to the production of multiple copies by alithographic duplicating process and it relates more particularly to themanufacture of a new and improved lithographic plate and to a new andimproved process for producing the ink receptive, water repellent imageon the lithographic surface of the plate.

Various methods are employed in the lithographic art for the formationof the ink receptive, water repellent image on a water receptive, inkrepellent surface of a lithographic duplicating plate. To the present,these processes may be divided into two principal groups generallyreferred to as the direct image process and the indirect orphotolithographic processes. In the direct process, an ink receptive,water repellent imaging material is applied directly onto thelithographic surface of the lithographic plate. For such purposes, thelithographic plate may be imaged by the use of a writing instrument forapplying the oleophilic, water repellent imaging material onto thesurface of the plate. Instead, the image may be formed on the plate bymeans of a typewriter or by a die, using a ribbon or a transfer sheetcoated with an ink receptive, water repellent imaging material which istransferred by the impressions from the transfer sheet to thelithographic surface to form the image thereon.

The indirect or photolithographic p ocess is used for the reproductionof copies from an original. In general, a photographic negative is firstproduced of the original and then the negative is exposed in combinationwith a lithographic plate in which the lithographic surface has beenpresensitized with a material such as a resin-forming diazo compound orwith a bichromate capable of tanning the colloid in combinationtherewith in the exposed areas whereby the exposed areas are convertedto an ink receptive, water repellent surface upon exposure to light toform the image thereon. The light sensitve materials remaining in theunexposed portions of the plate, or the non-imaged portions must beremoved, as by washing, before use can be made of the plate to producecopies.

The concepts described and claimed herein have application chiefly tothe indirect process for the production of .an imaged lithographic plateand the invention will hereinafter be described with reference to themanufacture and use of such a photolithographic plate.

Photolithographic plates of the type heretofore produced have beenconstructed chiefly with a surface sensitized with a light sensitivematerial, such for example as a resin-forming diazo compound which isconverted to an ink receptive, water repellent resinous material uponexposure to light. Such photolithographic plates formed with [lightsensitive diazo compounds are subject to dark or thermal decompositionreactions which results in overall ink receptivity or scumming. As aresult they have limited shelf life and it is necessary to prescribe anexpiration period of relatively short time in which the plate must beused.

Aside from the limited shelf life inherent in plates of the typeheretofore produced, the labor and equipment required for thepreparation of a photolithographic plate to produce the image thereonfrom an original are excessive and relatively expensive.

The more recently developed xerographic process for producing an imagedlithographic plate from an original embodies fewer limitations than thediazo-sensitized photolithographic plates, especially from thestandpoint of plate life and the character of the original, but theinitial investment in equipment required is excessive and the methodsfor preparing the masters are tedious and involved.

It is an object of this invention to produce a new and improvedlithographic plate and method for imaging same which is not subject toany of the deficiencies and disadvantages of the processes and productsheretofore employed.

More specifically, it is an object of this invention to produce a newand improved lithographic plate and process for imaging same and it is arelated object to produce a lithographic plate of the type describedwhich can be fabricated in a simple and eflicient manner; which isproduced of low cost and readily available materials; which is notlight-sensitive and therefore is not limited in time of use afterpreparation; in which the process enjoys the desired degree of exposurelatitude; in which the process has a broad range of spectralsensitivity; which does not require an initial investment of expensiveequipment for use in imaging the plate; which can be imaged in a simpleand eflicient manner from the original without an additional expenditureof time and labor; which has application chiefly as a postive workingphotolith-ographic plate; which may be used as a direct image plate, andwhich can be used to produce a large number of copies of good quality.

It is a further object of this invention to produce a lithographic plateand to provide a one-step photographic process for imaging same, and itis a related object to produce an imaged lithographic plate by aphoto-reflex process.

These and other objects and advantages of this invention willhereinafter appear and for purposes of illustration, but not oflimitation, an embodiment of the invention is shown in the accompanyingdrawing in which:

FIGURE 1 is a perspective view, partially in section, of aphotolithographic plate embodying features of this invention;

FIGURE 2 is a schematic elevational view illustrating the arrangement ofparts in an initial step of the process;

FIGURE 3 is a perspective View, partially in section, of the elementprepared by the step of FIGURE 2; and

FIGURE 4 is a schematic sectional elevational view illustrating a finalstep in the manufacture of the imaged lithographic plate.

In the Rott Patent No. 2,352,014, description is made of a single copyprocess wherein a photographic image of an original produced in a silverhalide layer is caused to produce a reverse image on a copy sheet,provided the silver halide layer, after being exposed to light for theproduction of a master image and then vbeing impregnated with adeveloper to' develop the image, is pressed or squeezed in the presenceof a fogging agent and a silver halide solvent onto the copy sheet whilethe layer is still imbibed with the developing liquid. That part of thesilver halide in the layer which was not reduced during developmentafter exposure to light and which in the ordinary photographic processwould be fixed out of the fixing bath, will adhere to and enter the copysheet surface by diffusion and will thus produce thereon a reversedimage. In order .to render this image freely visible, the lightsensitive layer containing the master image will nor mally be removedfrom the copy sheet.

In the Rott process, use may be made of the silver halide solventscontained in the usual photographic developers, such as sodium sulfite,sodium thiosulfate and the like. As fogging agents, use is made ofsubstances capable of promoting the reduction of silver halides withoutrequiring the action of light, such for example as colloidal silver,colloidal forms of sulphur, silver sulfides, hypophosphites, stannouschloride, and organic compounds which are capable of splitting offsilver in the form of bivalent ions, such as thiosinamine. Such foggingagents or nucleating agents are preferably embodied in the copy sheetduring manufacture thereof by subsequent impregnation.

It has now been found that when use is made of a nucleating agent forreduction of the silver halide, somewhat similar to the fogging agentsof Rott, instead of producing a reversed image as a single copy on areceptive material or copy sheet, a reversed image of an oleophilic orwater repellent image is formed which, when produced on a hydrophilic,water receptive lithographic surface, can be used to produce a largenumber of inked copies by conventional lithographic printing methods.

The reversed image of the oleophilic, water repellent or ink receptiveimaging material is formed by diffusion on the lithographic surface as areaction product when an alkali metal thiocyanate is present as aningredient dissolved in the development solution.

It is desirable to make use of a plate having a nonporous, non-absorbentsurface because the amount of complexed silver halide available fortransfer from the photographic image on the exposed negative or the likeis usually insuflicient to develop the desired image intensity on thesurface of the lithographic plate when portions thereof are capable ofbeing diffused inwardly into the interior of the plate.

Thus it is important to make use of a plate formed of metal such as zincor aluminum in the form of a rigid plate, sheet stock or foil which hasbeen treated on the printing surface for rendering the surfacehydrophilic, as by brushing, silicating, anodizing, etching, and thelike.

It has been found that the ink receptivity of the reversed image formedon the aluminum lithographic surface is markedly improved to produceinked copies of better quality when a soluble sulfide, such as sodiumsulfide, potassium sulfide or ammonium sulfide is present as a coatingon the surface of the lithographic plate.

Instead of sodium sulfide, use can be made of other soluble sulfidessuch as potassium sulfide and ammonium sulfide, as previously described,or water soluble compounds capable of releasing sulfide ions forreaction upon solution in the transfer medium.

By way of still further improvement, it has been found that the inkreceptivity of the reversed image and the anchorage of the oleophilicwater-insoluble image produced on the plate surface is increased by thepresence of lead ions on the lithographic surface, preferably in theform of a soluble lead salt, such as lead acetate, or other solublebivalent metal salts such as lead chloride, lead propionate, leadnitrate and similar salts of zinc, nickel, copper, cobalt and the like.Since the lead salts form insoluble compounds with the sulfides, it ispreferred, when used, to apply the lead as a coating onto thelithographic plate separate and apart from the sulfide. Theconcentration of metal salts is not critical as long as sufficient leadions are present in the coating to cause development of the desiredoleophilic material upon diffusion of the complexed silver halide fromthe photographic image.

The following is a description of the preferred practice of thisinvention:

Example I.Manufacture of the lithographic plate For use in the practiceof this invention, an aluminum sheet 10, the surface of which has beentreated by brushing, silicating, anodizing, etching or the like torender the surface lithographic, is coated with a solution containing 30parts by weight sodium sulfide in parts by weight of water. Applicationof the coating is made by any conventional process, such as by spraycoating, roller coating, brush coating and the like but it is preferredto coat the treated aluminum surfaces by means of a pair of squeegeerolls mounted to engage the opposite sides of continuous strips ofaluminum advanced in face to face relation from a pair of feed rolls.

The coating composition is applied in quantities sufficient tocompletely coat the surface of the aluminum to provide at least amonomolecular layer 11. The amount applied to the surface of the plateis such that the coating air dries within a very short time, such forexample as in about 10-30 seconds, without the necessity for usingelevated temperatures,

Following the first coating, the aluminum surface is subsequently coatedwith a 10 percent solution of lead acetate in water. Application is madein substantially the same manner as the first coating to provide a thinlayer 12 following which the sheet is dried, as by air drying, in arelatively short time such as from 10-30 seconds.

An aluminum sheet treated in the manner described is not sensitive tolight and thus may be manufactured in mass production processes inunlimited amounts and may be sheeted and packaged for subsequent use inthe manufacture of imaged photolithographic plates without limi-.tations as to the conditions of storage or the length of timeintervening between manufacture and use.

Example lI.--Preparati0n of the imaged master Description will now bemade of the use of the lithographic plate of Example I in thepreparation of an imaged master by print-through contact exposure froman original 14. First a photo-negative 15 containing a light sensitivesilver halide in a gelatin emulsion or the like hydrophilic colloidcoating 16 on a suitable base sheet such as paper or plastic film stockis exposed to an original by reflex or by print-through contact or byprojection printing to form a latent image in the silver halide gelatinemulsion. It is preferred in this process to make use of a photographicnegative which is transparent or translucent in order to give maximumlatitude of the original. The photographic negative does not have to beflexible and the thickness and dimension of the negative do not constitute important factors in the process. By way of example, a suitablephotographic negative is marketed by AGFA under the trade nameCopyrapid.

The exposed photographic negative is developed in a solution containingthe normal developing components plus a material which is a solvent forthe silver halide such as in a typical monobath developer including adeveloper and fixer such as are ordinarily employed in photographicpractice, a typical composition of which may be formulated of 30 gramshydroquinone, 30 grams sodium hydroxide, 40 grams sodium sulfite, 10grams sodium thiosulfate, 1.5 grams benzotriazole, with water sufficientto make up one liter. This development is carried out under suchconditions that the photographic negative wet with the solution and thephotolithographic surface wet with the solution are brought into surfacecontact with each other, as illustrated in FIGURE 4, so that the solublesilver complex that is formed of the silver halide in the photographicimage is caused to diffuse to the corresponding areas of thelithographic surface. Usually; contact under the conditions describedfor from /22 minutes is suflicient to effect the desired transfer forthe development of the reversed, oleophilic, water-insolw ble image onthe lithographic plate.

The. lithographic surface containing the nucleating agent in combinationwith sodium sulfide and/ or lead acetate promotes the reduction of thesilver halide complex without the action of light to produce anoleophilic, water-insoluble reaction product which is transferred orforms on the surface of the lithographic plate. The oleophilic reactionproduct formed in the areas corresponding to the original becomesstrongly anchored to the lithographic surface to form the image whichcan now be used to produce a large number of copies by lithographicduplicating technique. The printing plate may be lacquered by knowntechniques or printed without lacquer, as preferred, on an offsetlithographic press to produce exact and clear copies of the original.

In the presence of lead acetate or other soluble bivalent metal salts ofthe type described, with or without a soluble sulfide, almost any of thefogging agents of the type described in the Rott patent which willprecipitate soluble silver may be used to produce an ink receptive,water, repellent, reversed image on the aluminum lithographic surfacefor use in the production of multiple copies.

The following compositions may be employed in lieu of the lead acetatesolution applied as a second coating on the surface of the lithographicplate:

Example lII.5-15 percent by weight barium chloride in water ExamplelV.-520 percent by weight copper in water Instead of making use of aphoto-negative, it has been found that the gelatin coating sensitizedwith the silver halide may be applied as a coating directly onto thesurface of the aluminum lithographic plate which has previously beencoated with the desired materials for reaction to produce a desirablesilver compound with the silver salide. After exposure, the silverhalide in the unexposed areas corresponding to the image in the originalis caused to diffuse to the coated surface of the lithographic plateduring immersion in the developer for the exposed silver halide in whicha suitable solvent for the unexposed silver halide complex is present toenable diffusion.

Transfer of the silver halide in the processes described has been foundto cause adhesion of the lead salts and the formed reaction product withthe silver salts to the aluminum or other base of the lithographicplate. Upon formation of the water-insoluble, oleophilic image as areaction product, the gelatin is removed from the surface with warmwater.

By way of further modification, film forming agents such as watersoluble, hydrophilic colloids including gelatin, casein, polyvinylalcohol, the alginates and the like, may be formulated in small amountsin the initial coating composition for use as a film former adhesive toanchor the materials to the lithographic surface.

As previously indicated, the lithographic plate formed in accordancewith the practice of this invention can, if desired, be used as a directimage plate wherein the imaging material applied to the surface of theplate as a writing fluid or as a composition transferred by impact of atypewriter or die, contains a silver halide in solution capable ofreaction with thiocyanate or other reactive materials described on theplate surface to form the described water-insoluble, oleophilic,reaction product.

In sheeting, the plate may be formed to size with suitable openings inthe leading edges for attachment to the hooks provided on the platecylinder of a lithographic press, and the plates may also be formed withserrated trailing edges for engagement by the clamping means on theplate cylinder.

It will be understood that the concepts of this invention are notdependent on the concentrations of the various materials in the coatingcomposition so long as a uniform coating can be applied to the surfaceof the plate for deposition of a thin layer of the essential ingredientsthereon. It would be undesirable to make use of coating compositionshaving high concentrations of the salts or other materials such as inexcess of 30 percent by weight, since such large amounts are unnecessaryand such coating compositions might render the product and processuneconomical.

It will be understood that changes may be made in the details ofconstruction of the plate, formulation of the coating compositions, andthe method of application, and that changes may be made in the manner ofuse of the plate without departing from the spirit of the invention,especially as defined in the following claims.

We claim:

'1. A lithographic duplicating master consisting of an aluminum basesheet having a water receptive, ink repellent, hydrophilic lithographicsurface containing nuclei for precipitation of silver from a solublesilver complex and separate coatings on the aluminum lithographicsurface in which one of the coatings contains a water soluble salt of abivalent metal and the other coating contains a water soluble sulfide.

2. A lithographic duplicating master consisting of an aluminum basesheet having a water receptive, ink repellent, hydrophilic lithographicsurface containing nuclei for precipitation of silver from a solublesilver complex and a coat-ing on the hydrophilic lithographic surfacecontaining a water soluble sulfide and a second coating over the sulfidecontaining a salt of a bivalent met-a1.

3. A lithographic duplicating master consisting of an aluminum basesheet having a water receptive, ink repellent, hydrophilic lithographicsurface containing nuclei for precipitation of silver from a solublesilver complex and a coating on the hydrophilic lithographic surfacecontaining a water soluble sulfide and a second coating over the sulfidecontaining a salt of a bivalent metal selected from the group consistingof lead, zinc, nickel, copper and cobalt.

4. A lithographic duplicating master consisting of an aluminum basesheet having a water receptive, ink repellen-t, hydrophilic lithographicsurface containing nuclei for precipitation of silver from a solublesilver complex, a first coating on the hydrophilic lithographic surfacecontaining a salt of a bivalent metal selected from the groupconsist-ing of lead, zinc, nickel, copper and cobalt, and a secondcoating containing a water soluble sulfide.

5. A multiple copy process comprising the steps of applying an aqueousalkaline solution of a silver halide developer and a silver halidesolvent to a photo-exposed silver halide stratum and a superposedaluminum base sheet having a water receptive, ink repellent, hydrophiliclithographic surface containing nuclei for precipitation of silver froma water soluble silver complex, reducing the exposed silver halide inthe silver halide stratum to silver, forming from unreduced silver inthe silver halide stratum a water soluble silver complex, diffusing thecomplex to the lithographic surface of the aluminum base sheet,producing from the complex in conjunction with the nuclei a silver imagewhich is ink receptive and water repellent, stripping the silver halidestratum from the aluminum base sheet, wetting the aluminum base sheetwith an aqueous medium to wet out the water receptive, ink repellent,hydrophilic non-imaged portions of the aluminum base sheet, coating thealuminum base sheet with an ink which preferably wets out the silverimaged portions, and pressing the ink surface onto .a copy member forthe transfer of the ink image thereto.

6. The process as claimed in claim 5 in which the water receptive, inkrepellent, hydrophilic, lithographic surface of the aluminum base sheethas separate coatings one of which contains a water soluble sulfide andthe other of which contains a water soluble salt of a polyvalent metal.

7. The process as claimed in claim 6 in which the water soluble sulfideconstitutes a first coat on the surface of the aluminum base sheet andthe water soluble salt of a polyvalent metal comprises the second coat.

8. The process as claimed in claim '6 in which the water soluble salt ofa polyvalen-t metal constitutes a first coat on the surface of thealuminum base sheet and the water soluble sulfide comprises 'the secondcoat.

References Cited by the Examiner UNITED STATES PATENTS 5 OTHERREFERENCES 9/1896 Strecker 101-4492 Tritt'on: Pen-rose Annual, 1939, pp.107-111. 5/1939 Webb 101-1493 10/1942 Carlson 961 6/1944 Rim m 96 29NORMAN G. TORCHIN, Primary Exammer. 12/1954 Land 9629 10 D. LEVY,Assistant Examiner.

8 FOREIGN PATENTS 731,997 12/ 1931 France. 3,186,842 6/1965 GreatBritain.

1. A LITHOGRAPHIC DUPLICATING MASTER CONSISTING OF AN ALUMINUM BASESHEET HAVING A WATER RECEPTIVE, INK REPELLENT, HYDROPHILIC LITHOGRAPHICSURFACE CONTAINING NUCLEI FOR PRECIPITATION OF SILVER FROM A SOLUBLESILVER COMPLEX AND SEPARATE COATINGS ON THE ALUMINUM LITHOGRAPHICSURFACE IN WHICH ONE OF THE COATINGS CONTAINS A WATER SOLUBLE SALT OF ABIVALENT METAL AND THE OTHER COATING CONTAINS A WATER SOLUBLE SULFIDE.